1. Technical Field
The present disclosure generally relates to an electronic device including a display device, and more particularly, to a window member for a display device of a portable terminal and a method for fabricating the window member.
2. Description of the Related Art
In general, a portable terminal such as a mobile communication terminal, smartphone, portable multimedia device, etc., includes a display device to present images and information to the user. “Display device”, as used herein, includes light generating elements, e.g., pixels and their controlling electronics, touchscreen sensor elements (for touchscreen displays) and a transparent window member. The window member protects the display device and allows images to be transmitted therethrough. Hereinafter, a display device of a portable terminal will be referred to interchangeably as simply a “screen” of the portable terminal. A window member will be referred to interchangeably as simply a “window”.
A portable terminal may include a separate input device such as a keypad or track pad to input information. However, as various functions such as Internet access, multimedia reproduction, etc. have been recently incorporated into modern portable terminals, a trend has developed to include a touch screen function into the screen (this type of screen is referred to herein as a “touchscreen”). Thus a screen of sufficient size is mounted on the portable terminal for Internet access or multimedia functions, and in consideration of portability, functions of input and output devices have been implemented through the touchscreen, instead of including a separate input device. In this way, the portable terminal can be miniaturized while the size of the screen can be increased.
With the widespread use of portable terminals, effort has been steadily exerted to improve the user experience as well as functionality of the exterior of the portable terminal. As an approach to improve the user experience, a method for forming the screen as a curved surface has been proposed. For example, a screen having a slight concave surface at the edges of the screen may improve the feel of a smartphone along the contour of the user's cheek during a phone call. A concave surface may also allow certain images to be displayed with a unique or interesting appearance. The concave surface may be formed in just the lengthwise orientation of the screen.
Generally, the window member of a touch screen is frequently contacted by a user, so that the window needs to secure sufficient surface hardness. This need can be satisfied by using reinforced glass for the window. However, to minimize screen distortion, much time and cost are expended for processing the surface of the reinforced glass. Moreover, generation of a defect due to chips in the glass during processing lowers yield.
Therefore, a method for fabricating a window member as a curved surface by using an injection-molded product has been proposed. In the case of the injection-molded product, formation of one or more burrs in the fabricated injection-molded product is inevitable due to resin remaining in a mold gate. (A mold gate contains an aperture through which resin is injected to form the product; some excess resin inevitably remains attached to the product via the aperture after the resin forming the product hardens.) When the window member is fabricated with the injection-molded product to minimize formation of burrs, typically the mold is designed with only one melt-resin gate formed in the mold. Moreover, if the gate is disposed in the center of the mold for molding the window member, the screen is likely to be distorted. Therefore, it is desirable to position the gate in a portion of the mold corresponding to an edge of the window member, which is thicker than the central region. Further, to prevent the burr from being formed on an outer side of the window, i.e., the portion of the window that interfaces with a user, it is desirable to dispose the melt-resin gate on a portion of the mold interfacing with an inner side of the injection-molded product forming the window.
FIG. 1 is a side view of an injection-molded product 10 forming a window member according to the related art. An inner side 11 has a generally flat surface, and an outer side 13 has a curved surface such that the thickness of the window member increases toward both side ends thereof. A burr 19 is formed on the inner side 11 at a right end portion of the window, due to synthetic resin remaining in the melt-resin gate of the mold, as mentioned previously. The burr 19 is removable by separate processing such as grinding or the like.
However, since the window 10 is formed using only one melt-resin gate (not shown) disposed slantly toward a side of the mold, when the window is molded to have the curved surface, sufficient pressure is not delivered to the melt resin in a position far away from the gate, i.e., at the left end portion of window 10. As a result, the density of the window member is not uniform during hardening of the injected melt resin, or the injection-molded product shrinks in its portion to which the pressure for injecting the melt resin is not sufficiently delivered. These problems can cause deviation of the density or thickness distribution of the window member from a design requirement, eventually distorting the screen displayed through the display device.